JPS61177801A - Antenna system for automobile - Google Patents

Abstract

PURPOSE:To switch properly a main antenna and a sub-antenna and to obtain always stable receiving state by forming a high frequency pickup for detecting the output variation of the main antenna. CONSTITUTION:The main antenna 40 and the sub-antenna 42 for executing diversity reception are adhered to a rear glass 38 of a car body 38. On the other hand, a high frequency pickup 34 is arranged to previously detect the output variation of the main antenna 40 which is generated when the automobile is traveling on a position generating the steady waves of radio waves. When the pickup 34 detects the output variation of the main antenna 40 previously, and on the basis of forecasting that the level of the antenna 40 will be dipped after a certain time T, the antenna 40 is replaced by the sub-antenna 42 only for a dip generating period D. Consequently, always stable receiving state can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an antenna device for a vehicle, and more particularly to an improved antenna device for a vehicle that prevents fluctuations in the output level of a main antenna provided at the rear of the vehicle.

[Prior art] Generally, it is difficult to stably receive broadcast waves while a vehicle is moving, and FM radio waves at high frequencies in the VHF band travel in a strong straight line, resulting in direct waves and reflected waves reflected from buildings, mountains, etc. A multipath phenomenon occurs in which the signals interfere, causing distortion or momentary interruptions in the sound.

Therefore, conventionally, two antennas are placed on the car body at the required spacing, and the antenna with the better reception status is automatically switched to improve the directional characteristics of the antenna. A vehicle antenna device using a diversity reception method is known, which aims to reduce multipath noise due to the multipath phenomenon.

Some of the conventional vehicle antenna devices using the diversity reception method include two glass antennas provided at the upper and lower portions of the rear glass as a main antenna and a sub antenna constituting the diversity reception antenna.

[Problems to be Solved by the Invention] By the way, as shown in FIG. 9, the radio waves 12 emitted from the broadcasting station 10 are reflected from buildings 14, etc., where standing waves 16 are generated. When a vehicle receiving the radio waves 12 enters a place where such standing waves 16 are generated and the main antenna is located at a place where the standing waves hit, the output of the main antenna suddenly changes. However, the reception condition deteriorates.
At this time, with the conventional diversity reception method using two glass antennas provided on the rear window, it may not be possible to perform appropriate switching to improve the reception condition.

The present invention was devised in view of the above-mentioned conventional problems.The purpose of the present invention is to maintain the connection between the main antenna and the sub-antenna even in places where broadcast waves are reflected by buildings etc. and standing waves are generated. The purpose of the present invention is to enable appropriate switching of the signals and to always obtain stable reception conditions.

[Means and effects for solving the problem] In order to achieve this object, the present invention provides an antenna device for a car using a diversity reception method using two glass antennas attached to the rear glass of the car body. A high-frequency pickup is installed on the front pillar to detect a decrease in the output level of the main antenna in advance, and this high-frequency pickup detects a decrease in the output level of the main antenna in advance, so that the main antenna is activated after a predetermined period of time. The present invention is characterized in that it is equipped with an antenna switching signal generation circuit that predicts a dip in the output level and operates a switch circuit to switch to a sub-antenna that is not generating a dip, in a place where standing waves are generated. Also, the output level of the diversity antenna should be kept above a certain value.

[Example] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
First, a high frequency pickup, which is one component of the present invention, will be described.

10 to 15 explain the steps for determining the antenna device position with the highest efficiency by examining the distribution characteristics of high-frequency current.

FIG. 10 shows that when an external radio wave W such as a broadcast wave passes through a car body B made of a metal conductor, a surface current 1 corresponding to the strength of the 'R magnetic wave is induced in each part of the car body. Of these radio waves, the present invention targets only the frequency bands used for FM waves, television waves, etc. of 5oHuz or higher, which belong to relatively high frequency bands.

Then, in such a specific high frequency band, the induced current distribution of the vehicle body is measured, and high frequency pickups are installed in areas where the surface current density is high and there is little noise.A computer simulation is performed to understand the surface current distribution. Then, the actual current intensity is measured at each point. A probe based on the same principle as a high-frequency pickup installed in a desired part of the car body, which will be described later, is used, and this probe is spread over the entire surface of the car body at each point. The surface current was measured by moving it over the entire area while changing the direction from point to point.

FIG. 11 shows a schematic configuration of a probe P created based on almost the same principle as a high-frequency pickup described later, in which a case 10 made of a conductive material is used to avoid mixing of radio waves from the outside. Loop coil 1 inside
2 is fixed, an opening 10a is provided in a part of the case 10, a part of the loop coil 12 is exposed to the outside from this opening 10a, and the exposed part of the loop coil 12 is
It consists of a loop coil 12 that is placed close to the surface of the body B and detects the magnetic flux generated from the vehicle surface current.

A part of the loop coil 12 is connected by a shorting wire 14.
- the coaxial cable 18, and the output end 16 is connected to the core wire 20 of the coaxial cable 18. Further, a capacitor 22 is provided in a part of the loop coil 12, so that the frequency of the loop coil 12 can resonate to a desired frequency to be measured, thereby increasing the pickup efficiency.

As described above, by moving the probe P along the surface of the vehicle body B and rotating its angle at each measurement point, it is possible to accurately determine the surface current distribution and its direction on the vehicle body surface. In FIG. 11, the output of the probe P is amplified by a high frequency voltage amplifier 24, and the output voltage is measured by a high frequency voltage measuring device 26. This coil output voltage is read by the meter indication value of the measuring device 26, and the voltage corresponding to this meter indication value is recorded by the XY recorder 28 as a surface current distribution in each part of the vehicle body. The XY recorder 28 has a potentiometer 30
A signal indicating each position of the vehicle body is input from the sensor, making it possible to know the high-frequency surface current at each position.

FIG. 12 shows the declination angle θ between the high-frequency surface current I and the loop coil 12 of the pickup. V and generate the first
As shown in Figure 3, the maximum voltage is obtained when θ is 0, that is, the surface current ■ is parallel to the loop coil 12 of the pickup, and the surface voltage when the probe P is rotated at each measurement point and the maximum voltage is obtained! We can know the direction of r.

Figures 14 and 15 show the magnitude and direction of the high-frequency surface current generated in each part of the vehicle body at a frequency of 80H1lz, which was determined from both the measurement results with the probe P and the computer simulation. As is clear from the figure, the magnitude of the surface current exhibits a distribution in which the density is high in the portion along the edge of the flat portion of the vehicle body, and the density is extremely low in the central portion of the flat portion.

Furthermore, as shown in the current direction in FIG. 15, it is understood that each current is concentrated in a direction parallel to the edge of the vehicle body or along a connecting portion of each plane portion.

Furthermore, such a current density distribution indicates that the surface current is concentrated at a high density not only on the outer surface of the vehicle body B but also on the front pillar. As shown in FIG. 1, a high-frequency pickup 34 is provided on one front pillar 32 of the vehicle body to detect high-frequency surface currents flowing through various parts due to broadcast waves.

By the way, a main antenna 40 and a sub-antenna 42 for performing diversity reception are attached to the rear glass 38 of the vehicle body 36, and the above-mentioned high frequency pickup 3
Reference numeral 4 is provided to first detect the output fluctuation of the main antenna 40 that occurs when the vehicle runs in a place where standing radio waves are generated. Sub-antenna 42 where it is predicted that the level of 40 will dip and no dip has occurred.
The output level of the antenna is kept above a certain value by switching to

The structure of the high frequency pickup 34 provided on the front pillar 32 will be explained below based on FIGS. 2 to 4.

As is clear from the cross-sectional view of FIG. 2, it includes a pillar 32 and a pillar leg plate 44 formed into a hollow rectangular prism serving as its main pillar. A windshield molding 46 is fixed to the outer surface of the vehicle body of the pillar leg plate 44, and a windshield 48 is held on this molding 46.

Further, a weather strip rubber 50 is fixed to the rear side of the vehicle body of the pillar leg plate 44, and the rubber 50 ensures watertightness between the pillar leg plate 44 and the side glass 52.

Further, a front pillar garnish 54 is attached to the pillar leg plate 44 on the side facing the vehicle interior, which hides the surface of the pillar leg plate 44 and maintains an aesthetic appearance.

A high frequency pickup 34 is disposed on the front pillar 32 along the longitudinal direction of the pillar, and an electromagnetic coupling type high frequency pickup 3 is provided in the hollow interior of the pillar leg plate 44.
4 has been inserted.

As is clear from FIG. 3.4, the high frequency pickup 34 has a structure in which a loop antenna 58 is provided within a case 56 made of a conductor.The case 56 shields electromagnetic fields from the outside, but Opening 56 on the side
a, and from this opening 56a the loop antenna 58
Pillar where is exposed and high frequency surface current flows concentratedly,
In particular, it is arranged close to the pillar leg plate 44.

In the embodiment, in order to insert the high frequency pickup 34 into the hollow prism of the pillar leg plate 44, an opening 44a is provided in a part of the pillar leg plate 44, and the high frequency pickup 34 is inserted into the hollow prism of the pillar leg plate 44 before the front pillar garnish 54 is fixed. 34 is inserted internally into the pillar.

In order to fix the case 56 of the high frequency pickup 34 to the pillar leg plate 44, brackets 60 and 62 are fixed to both ends of the case 56 by spot welding or the like, and these brackets 60 and 62 are attached to the pillar leg plate as shown in the figure. 44, firmly tighten the screws.

Therefore, in this fixed upper plate, the loop antenna 5
8 is disposed in a position close to the opposite side of the opening 44a of the pillar leg plate 44, so that the magnetic flux caused by the high frequency surface current flowing intensively through the pillar leg plate 44 effectively interlinks with the loop antenna 58.

A circuit section 64 including a preamplifier and the like is built into the case 56 on the back side of the loop antenna 58 described above, and power and signals for controlling the circuit are supplied to this circuit section 64 from a cable 66. Further, the high frequency detection signal taken out by the loop antenna 58 is taken out from the coaxial cable 68 and processed by a circuit similar to that used in the surface current distribution described above.

In the embodiment, the loop antenna 58 is a single-turn antenna, and the coil is coated with an insulating coating so that it is placed in close contact with the pillar leg plate 44 in an electrically insulated state. A structure in which it is pressed against the edge is suitable, and the magnetic flux generated by the high-frequency surface current that flows intensively in the pillar can be efficiently linked to the loop antenna 58.

After the high-frequency pickup 34 is mounted in the front pillar 32 in the manner described above, the front pillar garnish 54 is attached to the pillar 32, and a structure that is no different in appearance from a normal pillar structure can be obtained.

Furthermore, when radio waves sent from a broadcasting station are reflected by a building or the like and a standing wave is generated, the dip interval of this standing wave is λ/, where θ is the angle between the direction of travel of the vehicle and the direction of arrival of the radio waves from the broadcasting station. 21 cos θ1, the distance between the high frequency pickup 34, the main antenna 40, and the sub antenna 42 is equal to the shortest distance λ/of the dip interval described above.
It is 2 or less.

Therefore, as shown in FIG.
, when a vehicle to which the main antenna 40 and the sub-antenna 42 are attached travels at a constant speed to a place where standing waves are generated, the respective outputs of the high-frequency pickup 34, the main antenna 40, and the sub-antenna 42 are shown in FIG. The dip generation point differs depending on the distance traveled, and the high frequency pickup 34. Each output 34a, 42a of the main antenna 40 and sub-antenna 42 has a dip point A.

The interval between B and C is the high frequency pickup 34. Main antenna 40. and the distance between the mounting positions of the sub-antennas 42.

Therefore, in Fig. 5, in the radio cassette, S/
Antenna output level L at which N deteriorates and noise is generated. If the points below are designated as C-, A-, and B-, the level of the high frequency pickup 34 is determined. Main antenna 4 after falling below
The time T until the point A' when the level of 0 drops below L is T = L24X1/, where the installation interval of the two antennas is L24
Vehicle speed...represented by ■. Also, the main antenna 40 is wide. The time limit is below . It is proportional to 1/vehicle speed.

In the present invention, the high frequency pickup 34 detects the antenna output fluctuation in advance, predicts that the level of the main antenna 40 will dip in one bale for a certain time, and prevents the dip from occurring for the duration of the dip. The antenna is switched to the sub-antenna 42 in an attempt to maintain the antenna output level above a certain value.

Next, the above-mentioned high frequency pickup 34 first detects the output fluctuation of the main antenna 40, predicts that the output level of the main antenna will dip after a predetermined FR plane interval, and suppresses the dip for the duration of the dip. An antenna switching signal generation circuit 70 that operates a switch circuit to switch to a subantenna that is not generating a signal will be explained with reference to FIGS. 6 and 7.

The output of the high frequency pickup 34 is input to a level comparator 72, which outputs a monopulse 100. After being reset by the pulse 100, the pulse counter 74 receives the pulse from the vehicle speed pulse generator 76 for one hour. A pulse 102 is generated every time corresponding to . The bistable multi-by-break circuit 78 generates a signal 104 by a pulse 100 which is an ON signal and a pulse 102 which is an OFF signal.

Further, after this signal 104 passes through the differentiating circuit 80,
A monostable multivibrator 82 driven with a negative voltage provides a signal 106 in which pulses are present only after one hour. On the other hand, the pulse counter circuit 84, which generates a pulse every time it corresponds to 0 time, is reset by the signal 106.

Thereafter, the signal 108 and the signal 106 from the pulse counter circuit 84 become the OFF signal and ON signal of the bistable multivibrator circuit 86, respectively, and the signal 108 and signal 106 from the pulse counter circuit 84 become the OFF signal and ON signal of the bistable multivibrator circuit 86, respectively.
A signal 110 is generated to set the N state.

Then, the switch circuit 88 changes from time BT to T+D by the signal 110 output from the antenna switching signal generation circuit 70.
This circuit has the function of switching from the main antenna 40 to the sub antenna 42 only during that period, and then switching to the main antenna 40, and the output 112 of the main antenna 40 or the sub antenna 42 is sent to the radio receiver.

Next, another embodiment will be explained with reference to FIG. In this embodiment, when the vehicle is backing up or stopped, broadcasts are listened to using the antenna with the best reception condition.

In the figure, the output of a switch 90 that outputs when the transmission is set to park or reverse is divided into two parts, one of which is connected to the antenna switching signal generation circuit 70 and the AND gate 92 shown in the previous embodiment, and the other is Connect to inverter 94. The output of this inverter 94 and the output of a level determination circuit 96 that uses the output of the intermediate frequency amplification device of the receiver to generate a signal when the signal is below a standard are connected to an AND gate 98. The output sides of the two AND gates 92 and 98 are connected to the OR circuit 120 and to the switch circuit 88.

According to such an embodiment, when the vehicle is in a running state, the operation shown in the above embodiment is performed to prevent deterioration of the S/N ratio,
When the vehicle is stopped or reversing, it is possible to always switch to an antenna with a good reception condition by comparing the levels of the two antennas 40 and 42, and it is possible to prevent S/N deterioration.

[Effects of the Invention] As explained above, according to the present invention, an antenna with a good reception condition is always selected even in a place where a standing wave is generated due to the radio waves of a broadcast wave being reflected by a pill or the like. , it becomes possible to obtain stable reception sensitivity.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the antenna mounting position of the automotive antenna device of the present invention, Fig. 2 is an explanatory diagram showing the schematic position of the high frequency pickup attached to the front pillar, and Fig. 3 is the same as shown in Fig. 2. Figure 4 is a cross-sectional view of the main part of Figure 3, and Figure 5 is a cross-sectional view of the electromagnetically coupled high-frequency pickup mounted on the front pillar. Figure 5 is a cross-sectional view of the high-frequency pickup, main antenna, and sub-antenna shown in Figure 1. Diagrams showing each output level, Figure 6 is a circuit diagram of an automotive antenna device, and Figure 7 is a circuit diagram of an automotive antenna device.
Each pulse waveform diagram in the figure, Figure 8 is an explanatory diagram showing another example, Figure 9 is an explanatory diagram showing the state of generation of standing waves due to the reflection of radio waves, and Figure 10 is an explanatory diagram showing the state of generation of standing waves due to the external wave W. surface current I
FIG. 11 is an explanatory diagram of a probe and its processing circuit for determining the distribution of car body surface current using a probe similar to the high-frequency pickup used in the present invention. FIG. 12 is an explanatory diagram of the surface current I and the pickup. An explanatory diagram showing the electromagnetic coupling state with the loop antenna, ° Fig. 13 is an explanatory diagram showing the directivity characteristics of the loop antenna in Fig. 12, Fig. 14 is an explanatory diagram showing the distribution characteristics of the surface current intensity, FIG. 3 is an explanatory diagram showing the direction of surface current. 32...Front pillar 34...High frequency pickup 40...Main antenna 42...Sub antenna 70...Antenna switching signal generation circuit. Applicant: Toyota Motor Corporation Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Q 7 T
+Q Figure 8 Figure 9 Figure 11 Figure 12 Figure 13 ■ Figure 14 Figure 15 , 6

Claims (1)

[Claims] (1) A main antenna installed at the rear of the vehicle body, a sub-antenna installed at the rear of the main antenna, and a high-frequency pickup installed at the front of the main antenna to detect output fluctuations of the main antenna first. Then, the high frequency pickup first detects the output fluctuation of the main antenna, predicts that the output level of the main antenna will dip after a predetermined period of time, and changes the output level of the main antenna to the sub-antenna, which is not generating a dip, for the duration of the dip. An antenna device for an automobile, characterized in that the antenna device includes an antenna switching signal generation circuit that operates a switch circuit to perform switching, and is configured to maintain the output level of a main antenna above a certain value.